1. Field of the Invention
This invention relates to a disc-shaped recording medium and a disc recording apparatus. More particularly, it relates to a disc-shaped recording medium for recording audio data by optical means, and a disc recording apparatus for recording audio data on such disc-shaped recording medium.
2. Description of the Prior Art
Among the disc-shaped recording media, such as optical discs, there are a plurality of types of discs, including a read-only disc, such as a compact disc (CD), a write-once type disc, on which data can be written only once, and a rewritable disc on which data can be re-written, such as a magneto-optical disc.
It may be contemplated that audio data processed by 16-bit straight quantization, with a sampling frequency of 44.1 kHz, be recorded on a user-recordable optical disc, such as the above-mentioned write-once type optical disc or magneto-optical disc, using a CD format, or a format with further data compression (CD-I format).
In these cases, the problem of copyright infringement is presented. That is, if audio signals can be recorded and reproduced as digital signals, dubbing may be effected many times without deterioration of the audio signals. Thus it becomes necessary to restrict recording in some way or other.
To this end, there are known a method of completely inhibiting dubbing of the audio signals as the digital signals, and techniques disclosed in JP Utility Model KOKAI Publication 2-46963 (1990) and JP Patent KOKAI Publication 2-83881 (1990) filed in the name of the present Assignee. Specifically, the former method, referred to hereinafter as a first technique, resides in prerecording or preformatting cumulative recordable time on an optical disc and recording cumulative recorded time up to the current time each time recording is made to restrict the recording when the cumulative recorded time exceeds the cumulative recordable time. The latter method, referred to hereinafter as a second technique, resides in dividing the user-recordable area of the write-once type optical disc into a number of subareas corresponding to the recordable number of tunes so that only one tune may be recorded in each subarea.
However, with the above-mentioned method of inhibiting dubbing of the digital signals, one of the usages of the magneto-optical disc or the like is lost. With the above-mentioned first technique, there is no problem when recording audio data in conformity to the CD-DA format. However, if recording is made in accordance with the CD-I format, that is if the audio data are recorded with data compression, the actual recording time is longer than that when recording is made in accordance with CD-DA format, even although the cumulative recorded time remains the same, so that the problem of partiality is raised. Specifically, the levels shown in Table 1 are prescribed in the CD-I format.
TABLE 1 ______________________________________ REPRODUC- QUANTIZED ING TIME SAMPLING NUMBER OF BAND- STEREO/ LEVEL FREQUENCY BITS WIDTH MONAURAL ______________________________________ A 37.8 kHz 8 17 kHz 2/4 B 37.8 kHz 4 17 kHz 4/8 C 18.9 kHz 4 8.5 kHz 8/16 ______________________________________
It is seen from Table 1 that, in the level B mode, for example, signals compressed to about 1/4 of the audio data of the standard CD-DA format are recorded or reproduced. This means that the recording time or the playback time may be fourfold.
On the other hand, with the above-mentioned second technique, the actually recordable time of music differs with different length of tunes, even although the number of tunes remains the same, so that again the problem of partiality is raised.